Surface finishing fixture



Nov. 28, 1950 R. A. SCHULTZ 2,531,921

SURFACE FINISHING FIXTURE Filed Dec. 26, 194"! 2 Sheets-Sheet 1 Y INVENTOR. RUSSEL A. SCHULTZ fl TTORNEY Nov. 28, 1950 R. A. SCHULTZ 2,531,921

SURFACE FINISHING FIXTURE Filed Dec. 26, 1947 2 Sheets-Sheet 2 INVENTOR. Russel. A. SCHULTZ -jected parts.

Patented Nov. 28, 1950 SURFACE FINISHING FIXTURE Russel A. Schultz, Detroit, Mich., assignor to Robbins Engineering Company, Detroit, Mich., a corporation of Michigan Application December 26, 1947, Serial No. 793,895

8 Claims. I

The present invention relates to a surface finishing fixture which is particularly adapted for the precision grinding and polishing of 19. workpiece having curvate surfaces and thin sharp edge portions which would be burned or scored by conventional grinding fixtures.

One type of workpiece which the present invention is particularly adapted to finish is a jet turbine blade comprising a conca'vo-convex spiral-form airfoil having thin sharp leading and trailing edges extending spirally and longitudinally of the blade at a spiral pitch which varies along the length of the blade. Such ablade is necessarily manufactured from an alloy steel adapted to withstand severe strains and high temperatures and is finished and polished'within high precision limits. A plurality of the finished blades are assembled on a jet rotor for rotation at a high angular velocity, so that aslight unbalancing of the rotor, resulting, forj'example, from lack of precision in the finished blades, will cause undue stress and wear in the turbine bearmgs.

A problem inherent in the economical grinding of jet turbine blades is that of grinding the spiral wherein it has been difiicult to reproduce the blade within the tolerances required. Checking and inspection of the blades thus formed are difficult and expensive operations, and the percentage of scrap or rejected blades has been high. By means of the present invention", spiralform turbine blades may be accurately ground and finished within machine tolerances of approximately .002, and the standard part and contour may be economically produced any desired number of times within these limits and with a minimum of scrap or rejected parts.

A primary object of the present invention is to provide a surface finishing fixture suitable for grinding and finishing the curvate contours of jet turbine blades by mass production methods, wherein the blade is economically formed according to a standard size and contour-within the high precision limits required and" with a minimum of waste resulting from scraper reall Other objects of the present invention are to provide a surface finishing fixture, adapted for simultaneously traversing and rotating a turbine blade across a flexible abrasive member adapted to conform to and grind the curvate contour of the blade as the latter is brought in contact therewith, to provide means in such a fixture for varying the grinding pressure on the blade accordingto its thickness so as to avoid scoring or burning the thin edges, and to provide means for automatically indexing the grinding pressure control mechanism in accordance with the spiral contour of the blade as the latter traverses the abrasive surface.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

In the drawings:

Fig. 1 is a right end elevation of the fixture embodying .the present invention.

Fig. 2., is a fragmentary enlarged horizontal section taken in the direction of the arrows substantially along the line 22 of Fig. 1.

Fig. 3 is a fragmentary front elevation, showing a partial section through the workpiece holder and taken in the direction of the arrows substantially along the line 3-3 of Fig. 2.

Fig. 4 is a fragmentary enlarged vertical section taken in the direction of the arrows substantially along the line 44 of Fig. 2.

Fig. 5 is an elevation of the broad side of a jet turbine blade which the fixture of the present invention is adapted to finish.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in' its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention-is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

' Briefly, the present invention proposes a work holding spindle mounted for moving a curvate workpiece by coordinated rotatable and axial movements across an abrasive member, the lat- -ter preferably comprisingan abrasive belt running at igh speed over a flexible rubber-like resilil y at theregion. of grinding-contact. The

work holding spindle is preferably mounted to permit a rocking movement of its axis of rotation toward and away from the abrasive member to permit variation of the grinding pressure on the workpiece and is subject to a constant yielding force tending to move the workpiece toward the abrasive member. In order to avoid scoring or burning of thin portions of the"- workpiece,v the grinding pressure is varied according to the thickness of the workpiece by pressure relief cam means, operating in coordination with the rota-- tion of the work holding spindle for selectively moving the latter away from the abrasive member against the aforesaid yielding force. Thus the axis of a workpiece, such as a turbineblade, having thin edges which would be injured if ground at the full grinding pressure applied at its thicker body portions, is gradually moved away from th abrasive member upon rotation of the thin edges toward the latter.

In; the situation of a spiral -form: turbine blade, the angular. position of the work holding spindle at which the blad'es edges approach the abrasive member varies as the blade moves axially. In a; preferred embodiment of the present invention, the pressure relief cam, restrained against 'axial movement, is rotatably mounted on' the work holding spindle: and rotated therewith by means of a' pin projected from" the pressure-relief cam and adapted to ride in a spiral cam-indexing slot carried by the work holding spindle upon" axial movement of the latter; The camindexing slot has a spiral pitch corresponding to the spiral pitch of the edge portions of the blade.

Thus as the. pressure relief ca m rotates with the work holding spindle, its angular position is indexed relative to the spindle in accordance with the spiral pitch of the edges of the workpiece as the latter is moved; axially across th abrasive member upon axial movement of the. spindle.

An embodiment of the present: invention particularly adapted for grinding and polishing the curvate surfaces of aspiral-form'jet turbine blade is shown by way of example in: the drawings and may be used to-perfornr these steps in the method of manufacturing such blades as disclosed in my co-p'ending application Serial No. 793,064, filed December 22, 1947. As shown in Figs. 1 and 3, a base If! supports an upright mounting IE to which is secured a vertical supporting plate 14. A bracket having the forwarqd' extending arms [-5 and base i=5 is secured by the plurality of bolts I! to the late M'and supports a bearing housing 1%. A spindle 20, which carries the relatively soft and flexible rubber-like mounting wheel 22, is suitably supported' and journaled within the housing F8. The mounting wheel 22, Fig. 2-, is secured to the extended left end of the spindle 29' for rotation therewith about a fixed axis and carries the abrasive belt 2 which is driven at a relatively high speed by the lower pulley 2 6; The latter is rotatably driven by the drive shaft 28 of the motor 30 mounted on the base Ill.

The bracket 32 is secured to the vertical plate slot 48 of the mounting 42 for rotation about the fixed axis of the pin 44. The pin 64 extends parallel to the axis of the mounting wheel 22 and is secured within the mounting 42 by the set screw 46. The left end of the pin 44 projects from the mounting 42 to support the upright guide 52, which is provided to prevent axial movement of the aforementioned grinding-pressure relief cam and which is secured to the mounting 42 by the screws 54.

Press-fitted within opposite ends of the stationary sleeve bracket 3 are the pair of cylindrical sleeve bushings for rotatably supporting the coaxial and longitudinally extending tube 58. The drive shaft fill, rotatably mounted Within and projected from opposite ends of the tube 58,115 concentrically spaced therefrom by the cylindrical spacer bushings 52 inserted within opposite ends of the tube 58 to the limit permitted by the annular shoulder 64 of each bushing 62. The right end: or the shaft 56- carries the'sl'eeve spacer 66 between the'corresponding shoulder 64 and balanced: crank arm 6?. The latter is suitably secured tortheend of the shaft (50 for rotation thereof and is balanced by the handle 68 and ball 69 secured to its opposite ends:

An: externally-threaded coaxial sleeve 1% is secured by the pin E2 to the left end of the shaft 6% for movement therewith "and; upon rotation of the shaft 5'12; imparts a screw-driven axial movement thereto by means of a screw-threaded engagement with the stationary internallythreaded: nut M. The latter is secured by the plurality-of-screws '16 to the sleeve bracket '55-, Fig. 2, which in turn is integral with the webbed bracket 11' secured to" the-verticalsupporting plate It: by the plurality of bolts l8, Fig. 3. Movementdimiting stops and 52 are adjustab'ly screw threaded on. opposite ends of the sleeve re; and secured thereto in adjust-ed positions b the set screws 8st and 86 respectively.

A movable sleevemounting 88- for a workpiece holding assembly is keyed by the key tdand pin' 92' to the tube 58 for rotation and axialmovemerit therewith. Extending laterally from the sleeve mounting 88 as an integral structure thereof isthe webbed bracket 9d for the bearing housing- 535 which journals and supports the spindle 83 having the pulley I66 secured axially toits-leftward extension for rotation therewith. The pulley IE8 is suitably driven by a belt H32 which in-turn' isdriven by the pulley ltd mounted on and rotatable with the shaft 6 3. The pulley we is disposed between the adjustable stop lfifi, secured by the pinill-3' to the-shaft 68' for rotation therewith, and the sleeve spacer H8 adjacent the left hand: shoulder E l.

An idler pulley 1 l2- rides on the belt I02 and is rotatably mounted on the shaft H4 extended through both the left hand web of the bracket 95 and the supporting bracket H5, which latter is pivotally mounted on the tube 53, Fig. 2. Coaxial spacers H8 and are provided around the shaft lit to suitably space-the pulley H2 and bracket Ht and'to space the-bracket l 56 from the adjacent web of the bracket Si l. The idler-pulley H2 is vertically adjustableby mean of the arouate adjusting slot E22 within the aforesaid left hand web of the bracket 9 Fig. l, to permit adjustment of the tension of the belt 522. The shaft H5 isclamped in its adjusted position within the arcuate slot 22 by the nut and washer assembly ['24.

At'the right of the bearing housing at, Figs. 2 and 3, the spindle 98 is secured to the work holding spindle I26 for rotation thereof, the latter providing the blade holding jig at its right end, including the detachable clamping member I28 which is interlocked with the end portion of the spindle I26 by means of the interlocking shoulders I32 and I36 of the members I26 and I28 respectively and is clamped in place by the clamping screw I33.

A jet turbine blade I34, illustrating the operation of the present invention, is shown in Fig. 5 and comprises the complex concavo-convex spiral-form airfoil having the longitudinally extending thin sharp leading and trailing edges I35 and I36, and also having the accurately machined dove-tailed base I31, which provides the machined indexing boss I33, and the nib I39 which provides the center hole I46. The base I31 with its boss I39, cooperable with the center hole I46, provide two points of indexing support for the blade I34 to assure its proper alignment within the blade holding jig for rotation about-a predetermined axis during the grinding' operation.

In the present instance, the blade I34 is preferably machined by suitable cam guided means to the general airfoil contour, so that grinding to its finished dimensions may be accomplished by a single pass across the high speed rotating abrasive belt 24. The clamping portions or the spindle I26 and the clamp I28 are suitably adapted to index with the boss I39 and to clamp the dove-tailed base I31, upon tightening the clamping screw I33, to permit rotation of the blade I34 about the axis of the center hole I 46 and coaxially with the axis of rotation of the work holding spindle I26. I

Rotatably mounted on the body of the blad holding spindle IE6 is the sleeve I4I which pro- .Vides the longitudinally extending spiral camindexing slot I42 and the relatively short circumferentially extending adjusting slot I43. The latter is adjustable along the clamping screw I44 which secures the sleeve I I-I to the spindle I26. Rotatably mounted on the sleeve MI is the cam sleeve I having the annular guide groove I46 which receives the upper extension of the guide member 52, thereby permitting rotational but preventing axial movement of the cam sleeve I45. The cam sleeve I65 provides the axially projecting indexing pin I46 which rides within the spiral cam-indexing slot I42, so as to key the sleeve 345 with the sleeve I II for rotation therewith and to index the angular position of the sleeve I45 relative to the spindle I26 as the latter moves axially. A pressure relief cam I59, having concavo-convex peripheral portions, Figs. 1 and 3, corresponding somewhat to the concavo-convex surfaces of the blade I34, is also carried by the indexing sleeve I45 and secured thereto by the screws I52, directly over the rotatable cam follower 59 for riding thereon at various angular positions of the cam I99.

With the blade I34 properly clamped by the clamp I28 at the end of the spindle I26 in coaxial alignment with the axis of the spindle I26, phantom view, Figs. 1 and 2, the center pin I54 will be spring-pressed into the indexing hole I49 to provide a second coaxial indexing support for the blade I34. In this position, the blade I34 will be directly over the belt 24 for grinding thereby upon operation of the fixture. The center I 54 is secured within the arm I 56 and in coaxial alignment with the spindle I26 by the set screw I58. The arm I56 is slidably mounted within the slot I69 of the plunger holder I62, which provides the center bore I 64 for receiving-the slidable plunger I66, and is secured by the bolt I68 to one end of the plunger I 66 for movement therewith parallel to the axis of rotation of the spindle I26. A spring well I19 opens within the other end of the plunger I66, Fig. 2, for the coil spring I12 which abuts the end cover I14 of the plunger holder I62 and coils around the guide stud I16 screwthreaded through the cover I14, the latter being secured to the plunger holder I 62 by the plurality of screws I18.

The plunger holder I62 is supported from the webbed bracket I89 which extends from the sleeve mounting I84 as an integral structure thereof. Similarly to the keying of the sleeve mounting 88 to the tube 58, Fig. 4, the sleeve mounting I84 is keyed to the tube 56 by the key I86 and pin I88 for both axial and rotational movement therewith. A lift arm I99 is provided for pivotally raising the bracket I89 and plunger holder I62 about the axis of the tube 58, being pivotally secured to the bracket I86 and plunger I66 by the vertical pivot pins I92 and I94 respectively for pivoting about their vertical axes. The pin I94 projects from the plunger I66 through a'longitudinal pin slot, not shown, provided therefor in the upper surface of the plunger holder I62 to permit longitudinal movement of the pin I94 with the plunger I66, and is adapted to support the weight I of the entire pivotally mounted blade holding assembly upon pivotally raising the arm I99. The slot I95, provided in the end of the arm I96 for the pin I92, permits a sliding movement of the arm I99 as the distance between the pins I92 and I94 varies upon sliding movement of the plunger I66. I

A vertically movable emergency pressure relief plunger I96 is provided directly below the bracket I86 for pivotally raising the latter. The plunger I96 is vertically movable within the sleeve I98 therefor which is supported from the bracket 290 projected from the bracket base I6. The lower portion of the plunger I96 projects through the bracket 29!! and is spring-pressed downward by the coil spring 262 which is under compression between the said bracket 269 and stop 294 secured to the lower end of the plunger I96. The lower extremity of the plunger I96 rests on one end of the pivotal lever 266, mounted on the horizontal pivot 296 disposed between the lateral webs of the bracket I5, Fig. 3. On the other side of the pivot 263 from the plunger I96, the lever 206 is pivotally connected at 2E9 to the coupling 2I2, which is secured to the tie rod 2I4 having the coupling 2 I 6 secured to its lower end and pivotally connected at 2I8 to the foot lever 226.

One end of the foot lever 226 provides the pedal 222. The other end is pivot-ally connected at 224 to the base I I It is apparent from the structure shown that the sleeve mountings 68 and I84, keyed to the tube 58, and their brackets 94 and I89, together with the bearing support 96, blade holding spindle I26, the plunger holder I62, and center pin I54, are all pivotally movable as a unit with the tube 58 about the horizontal axis of rotation of the shaft 66. The weight of the above pivotally mounted work holding assembly is directed to bear the workpiece I34 downward in grinding contact with the abrasive belt 24. In order to properly determine the maximum grinding pressure, the pivotally mounted work holding assembly is counterbalanced by the weight 228 adjustably mounted on the supporting arm 226 which is secured to the sleeve mounting 89 and projected radially therefrom oppositely to the. aforesaid iworkholdingassembly.

For a clear understanding: of the operation of the present invention, it to-be remembered that the. sleeve mounting. 34 and brackets I-I6 36, and: El are stationarily mounted on the upright mounting I2, whereas the sleeve mountings. 88 and IE4 are keyed to the; tube 58 for both rotation and linear movement: therewith. The shaft 60 is rotatable within the tube member 5'8-, but by virtue of the continuous sleeve linkages between the stop Hi5 and the crank arm 61., both secured to the shaft 80;, the tube 58 will necessarily move axially with the shaft 60.. Upon rotation of: the shaft 5.0,, the work holding spindle I126 will berotated by means of the belt I02, and the lead screw engagementbetween the threaded sleeve. 16 and the stationary nut-14 will drive the shaft 69 and tube 58 axially, resulting in parallel movement of the connected. work holding assembly, including the belt Ill-2, spindle I26, and center I354. Thus means are provided for simultaneously rotating and traversing the workpiece [34" relative to the portion of the abrasive belt 24 passing over the rubmr mounting wheel 22. The pitch of the screw feed is preferably adapted to move the workpiece I34 axially approximately the distance of the grinding swath of the abrasive belt. 2d upon each complete revolution of the spindle IZE, so that a new portion of the blade I34 will be continually brought to the grinding position until the entire surface thereof isground. By virtue of the flexibility of the mounting wheel '22, the abrasive belt 24 thereon readily conforms to the curvate contour of the workpiece I34, and av resiliency is provided at the region of grinding contact.

The relatively thick central portions of the blade I34 present no particular problem in the grinding operation At such portions, the pressure relief cam I58 does not ride on its follower 59,, and the full grinding pressure on the blade I134 is permitted, as determined by the counterbalanced weight of the work holding assembly.v As rotation of the blade I34 carries its relatively lower 50 and gradually rocks the work holding assembly away from the abrasive belt 24 about a pivot axis comprising the axis of rotation of the shaft GI]. Thus the grinding pressure is gradual-ly relieved and burning or scoring of the said M thin edges is avoided.

Finally as either of the edges I or I36 is rotated directly toward th grinding position, the blade I34 is removed completely from contact with the belt 24. Upon continued rotation of the blade I34, its other curvate surface is rotated toward the belt 24 and gradually rocked to the grinding position as the cam I5!) rides off the cam follower 5.9. As the thicker body portion of the blade I34 is rotated to the grinding position, the cam I59 rides clear of the follower and the maximum grinding pressure is again established.

its a consequence of the spiral-form contour of the blade $34., the angular position of the blade I34 at. which the edges 135 and I35 are rotated toward the abrasive belt 24 varies with the axial position of the blade I34. It is necessary to index the cam I59 continually in accordance with the. pitch of the spiral edges I35 and. I36 and the rate of axial movement of the blade I34.

Automatic indexing of the cam I50 is accomplished by the pin I48. riding within the.- spiral cam-indexing slot I42, so that. the rotation of the cam I50 is accelerated or decelerated' relative to the rotation of the blade I34 upon axial move.- ment of the sleeve I41! and work holding spindle I25 secured therewith. Thus the pressure. of the grinding contact is varied in accordance with the body thickness of the workpiece. At the same time, the indexing points for varying the grinding pressure are automatically varied in accordance with the contour of the blade and its axial movement relative to the abrasive belt24.

To facilitate removal or replacement of a workpiece I34 within the work holding assembly, the center I54 is retractable from the center hole I40 against the tension of the coil spring Il'2 upon pivoting the lever I counterclockwise about the pivot axis I 92, Fig.- 2. The grinding pressure may be released immediately at any time without recourse to the cam I58 by rocking the entire work holding assembly away from the belt 24, either by stepping on the pedal 222 and forcing the emergency relief plunger I96 upward against the underside of the bracket Hit, or by raising the lift arm I90.

It will be seen, therefore, that I have provided a surface finishing fixture suitable for the precision grinding of turbine blades or similar articles having complex spiral-form surfaces and thin edge portions subject to being injured when finished by conventional grinding operations. The fixture described permits the mass production finishing of turbine blades to tolerances of approximately .002, with a minimum of rejects or scrap parts. It permits the finishing of such blades from machined blanks and thus effects a considerable saving in manufacturing costs over precision casting or forging methods by which such turbine blades have been manufactured prior to the present invention.

Although the present invention is illustrated in connection with the grinding of jet turbine blades, it. is apparent that the fixture described may be utilized in the finishing of other curvate workpieces presenting problems similar to those involved in the manufacture of high precision jet turbine blades.

Having described my invention, I claim:

1. In a surface finishing fixture adapted for varying the grinding pressure on a workpiece according to the thickness thereof, the combination of an abrasive member for grinding a workpiece in contact therewith, a rotatable and axially movable workpiece holding spindle mounted for yieldingly moving the axis of rotation thereof to.- ward said abrasive member and for traversing a workpiece across said abrasive member .by coordinated axial and rotatable movements, pres sure relief cam means operatively coupled with said spindle for selectively moving the latter away from said abrasive member upon rotation of said spindle, and cam means for indexing said pressure relief cam means-relative to the angular position of said spindle upon axial movement of the latter.

2. The combination as claimed in claim 1 and being further characterized in that said pressure relief cam means include a fixed cam follower, and a pressure relief cam rotatably mounted on said spindle and held against axial movement for riding on said cam follower; and said indexing cam means include a cam-indexing slot carried by one of said members comprising said spindle andsaid pressure relief cam, and a projecting pin movable along said cam-indexing slot and carried by the other of said two members.

3. The combination as claimedin claim 1 and being further characterized in that the abrasive surface of said abrasive member is flexible and is resiliently supported, and in that said pressure relief cam is adapted to permit maximum grinding pressure at the relatively thick portions of said ,workpiece. and to. relieve the grinding pres sure at the thinner portions thereof.

4. In a surface finishing fixture, the combination of a rotating abrasive member, a rotatable and axially movable workpiece holding spindle pivotally mounted for rocking the axis of rotation thereof toward and away from said abrasive member for varying the grinding pressure on said workpiece, a lead screw operatively coupled with said spindle for feeding a workpiece held thereby to said abrasive member by coordinated axial and rotatable movements, means for yieldingly rocking the axis of rotation of said spindle toward said abrasive member, a fixed cam follower means rotatably mounted on said spindle and restrained against axial movement for rocking the axis of rotation of said spindle away from said abrasive member as the relatively thin portions of said workpiece are moved to the grinding: position and including a pressure relief cam adapted to ride on said cam follower, means to rotatably index said pressure relief cam relative to said spindle upon axial movement of said spindle and including a cam-indexing slot carried by said spindle, and a follower pin projected from said pressure relief cam for riding in said cam-indexing slot.

5. The combination as claimed in claim 4 and being further characterized in that said camindexing slot is provided within a sleeve adjustably mounted on said spindle for rotation therewith.

6. A fixture adapted for the precision grinding Of the concavo-convex spiral-form surfaces of a jet turbine blade having thin leading and trailing edges extending spirally and longitudinally of the blade, the combination of a rotating abrasive surface for grinding said blade, a longitudinally movable and rotatable blade holding spindle operatively coupled with a lead screw for coordinated axial and rotatable movement relative to said abrasive surface and being pivotally mounted for rocking the axis of rotation thereof toward and from said abrasive surface, means for yieldingly rocking the axis of rotation of said spindle toward said abrasive surface, a spiral indexing-cam slot provided by said spindle and having a spiral pitch corresponding to thp spiral pitch of the edges of said blade, a cam sleeve rotatably mounted on said spindle and restrained against axial movement, means for indexing said pressure relief cam in accordance with the longitudinal movement of said blade carried by said spindle and including a pin projected from said cam sleeve for movement along said indexingcam slot upon longitudinal movement of said spindle, a fixed cam follower, means to rock the axis of rotation of said spindle from said abrasive surface for gradually releasing the grinding pressure on said blade as the thin edges thereof are rotated toward said abrasive surface and including a pressure relief cam adapted to ride on said cam follower and secured to said cam sleeve for rotation therewith.

7. In a surface finishing fixture adapted for the precision grinding of a workpiece having relatively thin portions and relatively thick por tions and adapted for varying the grinding pressure on the workpiece to substantially reduce the grinding pressure applied to the thin portions of the workpiece, the combination of an abrasive member for grinding a'workpiece in contact therewith, a rotatable and axially movable workpiece holding spindle mounted f0! yieldingly moving the axis of rotation thereof toward said abrasive member and for traversing a workpiece across saidabrasivemember by coordinated axial and rotatable movements, a pressure relief cam means operatively coupled with said spindle for controlhpg the movement of said spindle toward and away from said abrasive member, said cam having a spindle engaging bearing surface providin a contour including portions corresponding to the contour of the thick portions of the workpiece which portion permit relatively high grinding pressures on the thick portions of the workpiece and also including portions which deviate from the contour of the thin portions of the workpiece and move the spindle away from the grinding member to reduce the grinding pressure on the workpiece while maintaining intimate contact therebetween for grinding the thin edge portions of the workpiece, and cam means for indexing said pressure relief cam means relative to the angular position of said spindle upon axial movement of the latter.

8. In a fixture for finish grinding the compound curvate surfaces of a blade having a relatively thick central body portion and thin spiral leading and trailing edges, the combination of a resiliently supported flexible grinding member a blade holding spindle mounted for coordinated axial and rotational movement for traversing and rotating a blade held thereby in grinding contact with said grinding member, said spindle and grinding member being operatively mounted for relative movement therebetween transverse to the axis Of rotation of said spindle, means for urging said spindle transversely of its axis of rotation toward said grinding member, and cam actuated grinding pressure control means adapted to prevent scoring of the thin edges of the blade and comprising cam means operatively coupled with said spindle for rotation and coordination therewith and adapted to effect said relative movement between said grinding member and the blade to permit the blade surface to be in grinding contact with said grinding member at a maximum grinding pressure during the grinding of the fixed central portion of the blade and at progressively reduced pressures during the grinding of the thinner portions thereof, and for interrupting the grinding contact between the blade and said grinding member near the periphcry of the thin edge portions of the blade whereby said edge portions are held out of grinding contact with said grinding member during rotation of said blade-holding spindle to bring the opposite face of the blade into grinding position, said cam means comprising a fixed cam follower, a sleeve cam rotatably mounted on said spindle for riding on said follower and restrained against axial movement and means to index said sleeve cam rotatably in coordination with the axial movement of said spindle and including a spirai indexing cam slot provided by said spindle and having a spiral pitch corresponding to the pitch of the spiral edges of said blade, and an indexing pin projecting from said sleeve-cam for movement along said indexing cam slot.

RUSSEL A. SCHULTZ (References on following page) REFERENCES CITED Nmnber The "following references are of record in the file o 1 pa ent 2,378,643 UNITED STATES PATENTS 2 409 32 Number Name Date 624,882 Unrich May 9, 1899 679,611 Ensign M 39, 1-901 Numbfil' 719,769 Ensign 1 Feb. 3,1903 97- 867 ,408 Phelps Oct. 1, 1907 Name 1mg I Beugler Mar. 1911 -Green June 13, 1944 Losey June 19, 1 945 Jakobsen Mary 21, 1946 F RE N fi 'lifiN' fi Golmtr-y Date Sweden 1-... Jan. 16,1910 

